Homeobox genes encode DNA-binding proteins that regulate the transcription of subordinate downstream genes, and thereby control a wide array of developmental events. An X chromosome-linked homeobox gene has been isolated that is expressed preferentially in reproductive tissue. In the testis, Pem protein is in the nuclei of Sertoli cells specifically during the androgen-dependent stages of the seminiferous epithelium cycle. In the epididymis, Pem transcripts localize to the region suggested to be involved in spermatozoa maturation. Published studies in mice and rats have demonstrated that Pem gene expression in the testis and epididymis is derived from a unique promoter (the proximal promoter [Pp]) that depends on androgen for expression in vivo. An independently regulated distal promoter (Pd) is responsible for expression in ovary and placenta, and to a lesser extent in the testis. Preliminary studies with transgenic mice expressing Pem ectopically from a tetracycline-regulated promoter have identified specific genes and events regulated by Pem. In this application, it is proposed (i) to elucidate the stage-specific function of Pem in Sertoli cells by examining the consequences of expressing Pem ectopically in Sertoli cells during all stages of the seminiferous epithelium cycle in transgenic mice, (ii) to identify genes regulated by Pem by screening for genes that exhibit altered expression in response to ectopic Pem expression in male reproductive tissues, and (iii) to identify cis- and trans-acting factors that dictate the unique expression pattern of Pem s male specific proximal promoter. The study of Pem gene function and regulation is important because Pem may be a transcription factor that regulates genes involved in androgen responsiveness, oxidative stress, proliferation, and apoptosis. An understanding of the role of Pem in reproductive function may lead to advances in the areas of fertility and birth control.